BuiltInMetadata.DistinctRowCount (Apache Calcite API)

All Superinterfaces:

Metadata

All Known Subinterfaces:

BuiltInMetadata.All

Enclosing class:

BuiltInMetadata
```
public static interface BuiltInMetadata.DistinctRowCount
extends Metadata
```
Metadata about the number of distinct rows returned by a set of columns in a relational expression.

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static interface BuiltInMetadata.DistinctRowCount.Handler
Handler API.

Field Summary

Fields
Modifier and Type Field Description

static MetadataDef<BuiltInMetadata.DistinctRowCount> DEF

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`java.lang.Double`	`getDistinctRowCount(ImmutableBitSet groupKey, RexNode predicate)`	Estimates the number of rows which would be produced by a GROUP BY on the set of columns indicated by groupKey, where the input to the GROUP BY has been pre-filtered by predicate.

Methods inherited from interface org.apache.calcite.rel.metadata.Metadata
rel

- Field Detail
  - DEF
```
static final MetadataDef<BuiltInMetadata.DistinctRowCount> DEF
```
- Method Detail
  - getDistinctRowCount
```
java.lang.Double getDistinctRowCount(ImmutableBitSet groupKey,
                                     RexNode predicate)
```
    Estimates the number of rows which would be produced by a GROUP BY on the set of columns indicated by groupKey, where the input to the GROUP BY has been pre-filtered by predicate. This quantity (leaving out predicate) is often referred to as cardinality (as in gender being a "low-cardinality column").
    
    Parameters:
    
    groupKey - column mask representing group by columns
    
    predicate - pre-filtered predicates
    
    Returns:
    
    distinct row count for groupKey, filtered by predicate, or null if no reliable estimate can be determined